The present invention relates to apparatus for automatic compensation of wear in a disc brake having floating shoes and to a brake utilizing this apparatus. The present invention more particularly concerns, but not exclusively, such a brake of the type for braking the shaft of an electric motor on which the disc is mounted and in which the release is electromagnetic.
It is known that in this type of brake (French Patent No. 14/79234) the shoes can slide axially with respect to the motor shaft, each on a side of the disc. For this, on one of the shoes, is fixed one of the extremities of the parallel guides parallel to the axis of the shaft and adapted to slide in specially prepared holders, as well as a support fixed to the motor housing while in the other shoe there are two holes receiving these guides which at the extremity opposite to that associated with the first shoe in turn traverses mountings in the yoke of the electromagnet before receiving means preventing withdrawal of the yoke from the guides.
The second shoe, called the front shoe, forms the armature of the electromagnet. Between the front shoe and the yoke of the electromagnet are mounted compression springs. With such a brake, when the electromagnet is energized, the front shoe is drawn toward the yoke and away from the disc which frees the disc.
Compensations means (French Patent No. 77/15458), such as springs interposed between the shoes and on each side of the support are generally known to the end that the front shoe withdraws from the corresponding face of the disc only through a distance substantially equal to one-half of the gap of the electromagnet so that the remaining action of this electromagnet is carried out by the yoke which will then move from the front shoe as from the disc and will thus permit the rear shoe to disengage the other face of the disc by the same spacing.
When the action of the electromagnet ceases, the front shoe directly undergoes the action of compression springs while the rear shoe is indirectly subjected thereto through the guides and these shoes press the disc and provide braking of the motor shaft. By reason of use, the linings of the shoes undergo certain wear and with greater use, on the one hand, the time of response is longer and, on the other hand, the compression springs are less and less compressed and their action becomes less efficient.
At the same time, the air gap increases and from this fact, at a certain time, the magnetic field might become insufficient to draw the armature.
To overcome these inconveniences, these brakes should be provided with means for taking up or compensating for wear which either require manual adjustment (Certificate of Addition French No. 95 911 of French Patent No. 14/79234), which unfortunately requires periodic surveillance of the brakes to measure their wear and so as to act on the various means of adjustment before the wear becomes excessive, or by acting automatically (French Application No. 69/45232 as well as German Application No. 2,314,483) as soon as the wear of the linings reaches a certain level and this is preferable.
In these documents, the means provided for this result, which in fact should limit the withdrawal of the front shoe and of the yoke on the guides, consist, carried by the front shoe and the yoke, of balls or conical washers automatically engaging on the guides when their displacement is carried out in the direction in which they leave the disc of the brake and they free the guides in the opposite direction.
Unfortunately, with these known means, the resulting wedging does not produce an adherent force sufficient to resist the strong axial push necessary for braking.
Further, at rest, vibrations or shocks can displace these washers on the guides and, for example, then prevent them from necessary withdrawal for disengagement of the brake.
To resist strong axial forces, it is known (French Patent No. 77/15458) to provide guides which are not smooth but have saw teeth positively wedging the washers in the appropriate direction.
Unfortunately, to obtain a fine adjustment, the teeth of the rack should have a very small interval so that the face of the stop of each tooth can be sufficiently inclined to tolerate a slight withdrawal of the shoes after passage of a tooth with the result that the disengagement of the brake is incomplete.
The present invention provides apparatus for automatic adjustment of a brake utilizable for motors where the braking force is large which always provides a sufficient play for the disengagement of the shoes.
To this end, the present invention has for an object apparatus of the type described which, to limit the movement of the front shoe and of the yoke with respect to the disc is characterized in that it comprises on each guide two stops and two wedges disposed in such a way that the front shoe and the yoke are so disposed that the face which is away from the disc engages one of these stops through one of the wedges which wedges are urged to interpose automatically, more and more between the face and the corresponding stop whereby these, in accordance with wear, are displaced one with respect to the other, the wedge only providing the displacement.